The league is called "The Faithful". It is possible to search the league list by name, and therefore access the complete list of accounts and ban them all in one go.
But to jump through the hoops....
Example castle can be found at -2855, -2359.
The castles directly above and below it on the map are all all from the same league and are also bots.
I did raise a support ticket. But I posted it hear because it's a pretty unique situation. No point just banning the single castle I reported. Support person needs to understand entire league is a serious problem and needs dealing with. That is best dealt with by explaining it here. Also we need feedback that is has been dealt with and how (which you don't get from support).
Thanks, in advance, for your help.
Of course, I can search for them. But it's not done this way. As I said, the best thing is to report this league to Support. So, thanks for submitting the ticket.
P.S. I can't disclose the results of our agents' investigation either.